For what I have in mind, initially, a non-requirement is perfectly mimicking whatever someone managed to jam into a standard, unless it's really necessary to use "necessary" sites.
(Anyone who does a lot of blocking of ads/trackers will already be familiar with sites not being pixel-perfect.)
I'm thinking that bending over to mimick someone's big-moat browser behavior standards in every detail can be a secondary priority, for later, after nerds are already using it successfully as a daily driver.
Nothing says nerds can't keep a Chromium installed as an emergency backup, for trying that one demo that uses the latest thing Google-Microsoft is going to railroad into the standard, or for watching Netflix while traveling. (And for Web development testing, of course.) But otherwise, we should be dogfooding, like we had to do with Linux.